This invention relates to a proportional mixing valve for mixing a hot and a cold fluid that includes a fail-safe mechanism for shutting off hot fluid flow when the temperature of the fluid exiting the valve exceeds a predetermined set point.
Mixing valves and fail-safe mechanisms in water and other fluid supply systems are well known. They are typically employed to control the maximum fluid temperature to a predetermined set point, which is usually a temperature, that is safe for human skin upon prolonged exposure. For example, hot water from water heaters typically has a temperature of 140xc2x0 F. to 160xc2x0 F. with a maximum temperature of 180xc2x0 F. At 140xc2x0 F., a child can be scalded if the skin is exposed for one second. However, if the water temperature is reduced to 120xc2x0 F. continuous exposure for five minutes is required to scald the skin.
In domestic applications, and in many commercial uses, it is desirous that the maximum hot water temperature from a shower, tub or basin outlets be set at a level that prevents serious burning or scalding of the skin. Oftentimes, a water faucet is allowed to run in a full flow hot water condition to purge cold water resting in the supply line to the faucet. A child or other unsuspecting person would be scalded if they were to contact the water once the cold water is purged. Thus, mixing valves are often used in the supply piping to basin, tub, or shower faucets in order to temper the hot water supply. Tempering the hot water supply at these point-of-use locations allows higher temperature water to continue to be produced by a water heater and used at locations where it is necessary, such as the washing machine or dishwasher.
While mixing valves temper the hot water supply under normal operating conditions, a fail-safe mechanism is necessary to isolate the flow of hot water when the supply of cold water fails. Serious injury could result to a child if, for instance, the cold water supply fails while the child is taking a shower, causing the water temperature to increase to its maximum supply temperature. Thus, fail-safe mechanisms can provide an added protective feature when combined with a mixing valve that is used to temper hot water.
Previous patents of mixing valves and fail-safe devices for hot fluid have employed various techniques. For example, U.S. Pat. No. 4,299,354 to Ketley discloses a thermally operated mixing valve. The temperature of the fluid is controlled via a thermally responsive control member that varies the flow of the cold fluid as needed to temper the hot water to the desired preset temperature. If the cold water supply fails or is interrupted, the control member reacts to either restrict or nearly isolate hot water flow. The valve is typically located at the point-of-use of the fluid supply since the user must manually operate the control member with an actuator to obtain fluid at a temperature less than the preset maximum temperature.
Another type of device is disclosed in U.S. Pat. No. 4,480,784 to Bennett and U.S. Pat. No. 3,938,741 to Allison. Each of these patents discloses safety devices for isolating water flow to an outlet when the water temperature exceeds a predetermined set point. Both devices are employed in the apparatus, which discharges the water, such as a showerhead. The Bennett devices employs a thermostatic cup that expands to constrict flow, but allows the hot water to drip so that the device continues sensing the water temperature. The Allison device includes a temperature responsive mechanism with a valve attached to one end that isolates flow when the water temperature exceeds a given operating temperature.
The foregoing prior art suffers from several drawbacks. For instance, the mixing valve device must be located near where the flow of fluid is controlled by the user. The devices also rely on a modulating control member to temper the hot water supply whose setting is controlled by the user""s manipulation of an actuator. In some valves, the fail-safe devices are required to be on or near a water supply system is required to temper the hot water supply temperature.
Another desirable feature absent from these prior systems is the ability to adjust the fluid temperature at the point-of-use outlet. Different maximum temperatures may be desirable at different discharge outlets, such as a kitchen sink versus a workroom tub.
What is needed, therefore, is a mixing valve assembly, which does not require modulating elements in order to temper the hot fluid supply. What is also needed is a mixing valve assembly, which includes a fail-safe mechanism that allows the valve to be used in virtually any location in a domestic or commercial water supply or fluid supply system.
A proportional flow mixing valve assembly is provided that allows a hot fluid supply to be tempered with a predetermined proportional flow of cold fluid based on the relative inlet diameters of the hot and cold fluid supplies. The assembly also includes a fail-safe mechanism, which isolates the hot fluid flow in case of interruption of the cold fluid supply. The assembly may also be provided with a check valve to prevent backflow of the hot fluid supply into the cold fluid supply in the event of its failure or interruption.
In particular, the assembly can mix a hot fluid with a cold fluid to achieve a mixed fluid that has a temperature below a specified threshold. The fluids are proportionately mixed in a mixing chamber in order to temper the hot fluid temperature. The desired temperature is obtained based on the sizing of relative inlet diameters allowing proportional flow from the hot and cold fluid inlets. When the cold fluid supply is interrupted or fails, a failure responsive means isolates the hot fluid flow when the mixed fluid temperature in the mixing chamber exceeds a predetermined set point temperature. The set point temperature is typically set such that the mixed fluid temperature will be safe with prolonged exposure to the human skin.
The failure response means includes a fail-safe mechanism, which is biased in an open position. The fail-safe mechanism can include a housing containing a thermally responsive medium, which volumetrically reacts to changes in the fluid temperature in the mixing chamber. The thermally responsive medium is engaged to a plug, which moves toward the hot fluid inlet as the fluid temperature increases. When the fluid temperature exceeds a predetermined threshold, the plug isolates the hot fluid supply. The valve assembly may also include a check valve in the cold fluid inlet to prevent backflow or siphoning upon failure or interruption of the hot fluid supply.
In a further embodiment, a flow control member is interposed at one of the fluid inlets, such as the cold inlet. The flow control member is adjustable to permit adjustment of the limit temperature of the mixed fluid discharged from the valve. the adjustable flow control member can include a stepped diameter screw that is advanced across the inlet fluid flow to reduce the flow in relation to the stepped diameter. This adjustable flow control member does not interfere with the fail-safe functioning of the valve, but instead allows the user to specifically determine the maximum mixed fluid temperature at a particular fixture or faucet.
One object of the present invention is to provide a mixing valve in which the relative diameters of the fluid inlets are proportionately sized to control the mixed fluid temperature below a safe threshold temperature. Another object of the present invention is to provide a fail-safe assembly that isolates hot fluid flow then the mixed fluid temperature exceeds the threshold level due to, for instance, failure of the cold fluid supply.
It is yet another object of the present invention to provide a fail-safe proportional mixing valve with a means for preventing backflow into a failed or low pressure fluid supply line from the intact supply line. A further object is accomplished by features that permit adjustment of the maximum mixed fluid temperature discharged from the mixing valve assembly, without sacrificing the fail-safe features of the assembly.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment and the accompanying figures.